Melting Permafrost Is Dumping Toxic Metal Into Alaska’s Rivers

The above image isn’t a heat map, despite its bright colors. Instead, it’s a photograph of Kutuk River in Gates of the Arctic, a vast national park in the remote northern region of Alaska. As Arctic permafrost melts, toxic metals leach into several of the state’s rivers, turning the water orange and highly acidic. New research reveals the extent to which permafrost melt affects Alaska’s waterways, profoundly changing nearby ecosystems, utilities, and industries.

Permafrost is supposed to be a permanently frozen layer of Earth’s crust. In areas like the Arctic, permafrost has existed for thousands of years on land and below the ocean floor. Thanks to climate change, however, permafrost is having a tough time sticking around. As the air and water around it warms, it melts, releasing everything from ancient pathogens to caches of toxic metals into the surrounding environment. 

To measure melting permafrost’s effect on nearby waterways, ecologists with the National Park Service snapped aerial images of Alaska’s Brooks Range, home to more than 75 once-pristine rivers and streams. As they flew over the range, the team “started noticing more and more orange rivers,” according to ecologist Jon O’Donnell. “There are certain sites that look almost like a milky orange juice.”

A headwater tributary of the Akillik River in August 2017 features far less permafrost pollution than it did in August 2018.
Credit: O’Donnell et al, Communications Earth & Environment/10.1038/s43247-024-01446-z

The orange water isn’t just an eyesore. It’s a sign of severe environmental degradation marked by toxic metals. In a study published in Communications Earth & Environment, O’Donnell’s team reports that the orange waterways have lower pH, higher turbidity (or murkiness), and higher concentrations of sulfate, iron, zinc, nickel, copper, and cadmium than rivers and streams that haven’t turned orange. It’s the iron that contributes to polluted streams’ discoloration, but unusual concentrations of other metals can be highly toxic to stream biota, such as fish, algae, fungi, plants, and even some mammals.  

“The stained rivers are so big we can see them from space,” said Brett Poulin, an environmental toxicologist and one of the study’s principal investigators. 

The polluted rivers and streams are already impacting other parts of the Brooks Range ecosystem. “Stream discoloration was associated with dramatic declines in macroinvertebrate diversity and fish abundance,” the study reads. In one example, the researchers noted a highly acidic seep in the Agashashok River basin. Downgrading the seep, they found vegetation “blackened and dead,” likely due to the water’s harsh acidity. The researchers also write that permafrost thaw could have “unforeseen risk” for food security as many Alaska residents rely on subsistence fisheries and local drinking water supplies. 

O’Donnell, Poulin, and their colleagues hope to promote rebound research to investigate whether (and how) rivers and streams could recover from such dire pollution. Right now, it’s expected that permafrost will continue to melt. But if cold weather can help melting permafrost solidify, it could buy waterways some time to regroup.